This invention relates to a drive shaft for a motor vehicle, especially plural shafts are connected together by a coupling that absorbs an oscillation of the drive shaft in an axial direction of the drive shaft. Since the drive shaft frequently receives an oscillation in the axial direction, the coupling is provided between the shafts in order to absorb the oscillation that would cause a vibration of a motor vehicle.
This type of drive shaft generally is known. For example, relevant related art is disclosed in Japan Utility model publication (koukai) No. 63-178632. This publication discloses an output shaft, an input shaft and a coupling. One end of the output shaft is connected to a transmission of a motor vehicle and one end of the input shaft is connected to a rear axle of the motor vehicle. The other end of the output shaft and the other end of the input shaft are connected together through the coupling. According to this publication, the coupling is made of rubber material.
As shown in FIGS. 10 and 11 illustrating a relevant related art, a coupling comprises a main body 1 made of rubber material and formed in an annular shape. Six bushings 2 are provided on an outer periphery of the main body 1 so that all of the bushings are provided in the same interval in a circumferential direction. Every mutually adjoining two bushings 2 are connected together by a wire 8 made from a material that has a high-rigidity, for example, glass fiber. A first yoke 5 that has three arm portions 5a is fixed to an end of an output shaft 3. A second yoke 6 that has three arm portions 6a is fixed to an end of an input shaft 4. The yokes 5 and 6 are formed by forging. The arm portions 5a and 6a are fixed to the bushings 2 by bolts 12 so that the bushings 2 are fixed alternately to the arm portions 5a and 6a in the circumferential direction. The end of the output shaft 3 extends through a center of the main body 1 and is supported by supporting rubber 7 provided on the yoke 6 so that an axis of the output shaft 3 and an axis of the input shaft 4 coincide.
According to this type of coupling, every mutually adjoining two bushings 2 are connected together by the wire 8 and the main body 1 is made of rubber material. Hence, a relative displacement between the output shaft 3 and the input shaft 4 in an axial direction of the input shaft 4 is permitted by the main body 1 while a revolution of the output shaft 3 is transmitted to the input shaft 4 without losing power by virtue of the tension of the wire 8.
However, since a structure of this type of coupling tends to be complicated, and thus, a size of this type of coupling become large, another type of coupling that has an annular plate instead of the rubber material as the main body has been provided. This type of coupling is disclosed in, for example, Japan Utility model publication (koukai) No. 60-189620. The annular plate of this type of coupling is also shown in FIG. 12 of the present invention.
As shown in FIG. 12, an annular plate 9 has six hole portions 10. The hole portions 10 are provided in an outer periphery of the annular plate 9 so that all of the hole portions are provided in the same interval in a circumferential direction of the annular plate 9. Three arm portions 12 of a first yoke (not shown) are provided on an output shaft (not shown) and three arm portions 13 of a second yoke (not shown) are provided on an input shaft (not shown). The arm portions 12 and 13 are fixed to the annular plate 9 by bolts (not shown) so that each arm portion 12 and 13 is fixed alternately to the annular plate 9 in the circumferential direction of the annular plate 9. The annular plate 9 is made of metal that has a rigidity and is formed so that a thickness in an axial direction of the annular plate 9 is equal at all portions. There are provided washers 11 on the hole portions 10.
Assuming that a portion connecting every mutually adjoining two holes 10 is called connecting arm portions 9a, the connecting arm portions 9a absorb oscillation that occurs in an axial direction of the output shaft and transmit a revolution of the output shaft to the input shaft without losing power. Further, since the annular plate 9 is made of material that has a rigidity, the output shaft and the input shaft are connected so that both axes of the output shaft and the input shaft coincide without adding any means for arranging the axis of one of the output shaft and the input shaft to the axis of the other of the output shaft and the input shaft.
However, since both yokes are formed by forging, each yoke tends to be heavy and some after-processes, such as a drilling process for making the hole portions 10 and a cutting process for providing a flat surface at which the yoke is connected to the coupling, are necessary. As a consequence, a drive shaft tends to be heavy and expensive.
Accordingly, in view of above-described problems encountered in the related art, a principal object of the present invention is to provide a drive shaft that has a lightweight yoke.
Another object of the present invention is to provide a drive shaft that has an easily assembled yoke and coupling.
Still another object of the present invention is to provide an inexpensive drive shaft that has durability.
In order to achieve these and the other objects, there is provided a drive shaft that comprises a first shaft comprising a first yoke fixed to an end of the first shaft, a second shaft comprising a second yoke fixed to an end of the second shaft. The second yoke being made of a metal plate by press-forming. A coupling is provided between the first yoke and the second yoke. The coupling has a high-rigidity in a rotating direction of the drive shaft and has an elasticity in an axial direction of the drive shaft.
Other aspects and advantages of the invention will become apparent from following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principle of the invention.